Experimental comparison of repeatability metrics

Peter Gagliardi and Don C. Lawton

ABSTRACT

Time-lapse experiments were performed on the nrms repeatability
(NRMS), predictability (PRED) and signal to distortion ratio (SDR)
repeatability metrics, and the results studied in order to better
understand their meaning. First, controlled time-shift, amplitude and
additive noise perturbations were made to a baseline seismic
trace. Time-shift had approximately linear effects on NRMS of about
15%/ms, subtle hyperbolic effects on PRED and a negligible effect on
SDR. Amplitude tests showed that multiplication of the baseline trace
by 0.9 resulted in an NRMS value of 10.5% and SDR value of 10
2.04
,
while PRED remained unaffected by any amplitude change; analytic
equations were found to relate amplitude changes to these
metrics. Additive noise experiments revealed that NRMS and PRED are
very sensitive to the strength and character of the noise, while SDR
seems to be affected little by the noise character.

Second, all three metrics were calculated using a 2D walkaway vertical
seismic profile (VSP) dataset from Violet Grove, Alberta, which
consisted of three lines. For Lines 1, 2 and 3, NRMS values were
60.6%, 61.4% and 45.2% for horizontal components, and 46.3%, 42.6% and
41.4% for the vertical component. PRED was 0.73, 0.72 and 0.83 for the
horizontal components, and 0.82, 0.83 and 0.87 for the vertical
component. Finally, SDR was 10
0.38
, 10
0.29
and
10
0.70
for the horizontal components and 10
0.74
,
10
0.85
and 10
0.79
for the vertical
component. The trends of these metrics, while similar, do not always
agree with each other, and should be used in tandem to better
understand the repeatability metrics of time-lapse data.